The possibility to determine the position of a mobile device has enabled application developers and wireless network operators to provide location based, and location aware, services. Examples of those are guiding systems, shopping assistance, friend finder, presence services, community and communication services and other information services giving the mobile user information about their surroundings.
In addition to the commercial services, the governments in several countries have put requirements on the network operators to be able to determine the position of an emergency call. For instance, the governmental requirements in the United States of America (USA), such as Federal Communications Commission Emergency 9-1-1 (FCC E911) that it must be possible to determine the position of a certain percentage of all emergency calls. The requirements make no difference between indoor and outdoor environment.
In many environments, the position can be accurately estimated by using positioning methods based on Global Positioning System (GPS). However, GPS-based positioning may often have unsatisfactory performance e.g. in urban and/or indoor environments. Complementary positioning methods could thus be provided by a wireless network. In addition to User Equipment-based (UE-based) Global Navigation Satellite System (GNSS including Global Positioning System, GPS), the following methods are available in the Long Term Evolution (LTE) standard for both the control plane and the user plane,                Cell Identification (CID),        Evolved-CID, such as E-CID including network-based Angle of Arrival (AoA),        Assisted-GNSS including Assisted-GPS,        Observed Time Difference of Arrival (OTDOA),        Uplink (UL) Time Difference of Arrival (UTDOA)—being currently standardized.        
TDOA-/TOA-based methods, e.g. OTDOA, UTDOA or GNSS/A-GNSS: A typical format of the positioning result is an ellipsoid point with uncertainty circle/ellipse/ellipsoid which is the result of intersection of multiple hyperbolas/hyperbolic arcs (e.g. OTDOA) or circles/arcs (e.g. UTDOA, GNSS, or A-GNSS).
Hybrid methods: Since the hybrid technique involves a mix of any of the methods above, the position result can be any shape, but in many cases it is likely to be a polygon.
Cellular positioning methods often rely on knowledge of anchor nodes' locations, e.g., evolved Node B (eNodeB) or beacon device locations for OTDOA, Location Measurement Unit (LMU) antenna locations for UTDOA, eNodeB locations for E-CID. The anchor nodes' location may also be used to enhance Adaptive Enhanced Cell ID (AECID), hybrid positioning, etc.
Dead Reckoning (DR), aka deduced reckoning, is the process of calculating one's current position by using a previously determined position, or fix, and advancing that position based upon known or estimated speeds over elapsed time, and course.
In cellular networks, GPS receivers with dead reckoning are used during GPS unavailability period, e.g., in tunnels, parking garages, and other common situations. When the GPS signals are restored, the dead-reckoning solutions may also provide a starting point for the GPS receiver configuration to search for GPS signals.
Three types of GPS receivers that support dead reckoning are known:                GPS receiver that utilizes vehicle speed signal input        GPS receivers utilizing wheel rotation data, where vehicle's speed and steering direction is estimated from wheel rotation data        GPS receiver with integrated inertial sensors, e.g., gyro sensor or acceleration sensor.        
The disadvantage with dead reckoning based on GPS is mandating GPS receivers which may be not affordable e.g. for low-cost wireless devices.
The three key network elements in an LTE positioning architecture are the Location Service (LCS) Client, the LCS target and the LCS Server. The LCS Server is a physical or logical entity managing positioning for a LCS target device by collecting measurements and other location information, assisting the terminal in measurements when necessary, and estimating the LCS target location. A LCS Client is a software and/or hardware entity that interacts with a LCS Server for the purpose of obtaining location information for one or more LCS targets, i.e. the entities being positioned. LCS Clients may reside in a network node, external node, Public Safety Answering Point (PSAP), user equipment (UE), radio base station, etc., and they may also reside in the LCS targets themselves. An LCS Client (e.g., an external LCS Client) sends a request to LCS Server (e.g., positioning node) to obtain location information, and LCS Server processes and serves the received requests and sends the positioning result and optionally a velocity estimate to the LCS Client.
Position calculation can be conducted, for example, by a positioning server, e.g. Evolved SMLC (E-SMLC) or Secure User Plane Location Platform (SLP) in LTE or UE. The latter corresponds to the UE-based positioning mode, whilst the former may be network-based positioning (calculation in a network node based on measurements collected from network nodes such as LMUs or eNodeBs) or UE-assisted positioning (calculation is in a positioning network node based on measurements received from UE).
FIG. 1a illustrates the UL positioning architecture specified by 3rd Generation Partnership Project (3GPP). Although UL measurements may in principle be performed by any radio network node (e.g., eNodeB), UL positioning architecture may include specific radio network nodes such as UL measurement units (e.g., LMUs) which e.g. may be logical and/or physical nodes, may be integrated with radio base stations or sharing some of the software or hardware equipment with radio base stations or may be completely standalone nodes with own equipment (including antennas). The architecture is not finalized yet, but there may be communication protocols between LMU and positioning node, and there may be some enhancements for LTE Positioning Protocol A (LPPa) or similar protocols to support UL positioning. A new interface, “SLm”, between the E-SMLC and LMU is being standardized for uplink positioning. The interface is terminated between a positioning server (E-SMLC) and LMU. It is used to transport SLmAP, aka LMUp, protocol messages over the E-SMLC-to-LMU interface. Several LMU deployment options are possible. For example, an LMU may be a standalone physical node, it may be integrated into eNodeB or it may be sharing at least some equipment such as antennas with eNodeB—these three options are illustrated in the FIG. 1a. 
LPPa is a protocol between eNodeB and LCS Server specified only for control-plane positioning procedures, although it still can assist user-plane positioning by querying eNodeBs for information and eNodeB measurements.
In LTE, UTDOA measurements, UL RTOA, are performed on Sounding Reference Signals (SRS). To detect an SRS signal, LMU needs a number of SRS parameters to generate the SRS sequence which is to be correlated to receive signals. SRS parameters would have to be provided in the assistance data transmitted by positioning node to LMU; these assistance data would be provided via an Application Protocol referred to as SLmAP (SLmAP), aka Location Measurement Unit protocol (LMUp), as defined in 3GPP TS 36.456/36.459. However, these parameters are generally not known to the positioning node, which needs then to obtain this information from eNodeB configuring the SRS to be transmitted by the UE and measured by LMU; this information would have to be provided in LPPa or similar protocol.
In FIG. 1b, architecture for downlink (DL) positioning according to prior art is illustrated.
Positioning Quality of Service (QoS) normally refers to two aspects of requirement: positioning accuracy and response time. The importance of each of the two quality characteristics is that they are generally service- and LCS application dependent. Often the positioning accuracy is of a more importance and typically it is the bottleneck in implementation.
Accuracy, and confidence, is important in several parts of the positioning system. First, when a positioning request arrives from the end user to the positioning node, a decision on which positioning method to use needs to be taken. The positioning node then needs to look up prior accuracies of the available positioning methods and compared these to the signaled requested accuracy from the end user, in order to select a most suitable positioning method. Then when a positioning results is available, the achieved accuracy is computed in the positioning node and it is determined if the requested accuracy was met. If so the positioning node reports the result and possibly the accuracy, back to the end user. If not met, the positioning node may proceed with a positioning re-attempt or another positioning method.
Positioning QoS may be of two types:                Target positioning QoS, aka target LCS quality, which may be associated, e.g., with the LCS Client type or service type and is typically known prior positioning method selection, e.g., received by positioning node from MME or obtained by a pre-defined rule,        Positioning result QoS or positioning result quality, which needs to be distinguished from positioning measurement quality; there may be multiple measurements used for positioning of the same UE, and each measurement is characterized with own quality; the set of measurements and their qualities also impact the positioning result quality, but measurement quality is not the same as the positioning result quality.        
AECID is one kind of fingerprinting positioning technology that refines the basic cell identity positioning method in a variety of ways. It is Ericsson proprietary.
The AECID positioning method is based on the idea that high precision positioning measurements, e.g. A-GPS measurements, can be seen as points that belong to regions where certain cellular radio propagation condition persist.
Step 1: A-GPS positioning is performed at the same time of UE network signal measurement. The AECID positioning method introduces a tagging of high precision measurements according to certain criteria, e.g. including                The cell Ids that are detected by the terminal, in each grid point.        Quantized path loss or signal strength measurements, w.r.t. multiple RBSs, performed by the terminal, in each grid point.        Quantized Round Trip Time, such as Round Trip Time in Wideband Code Division Multiple Access (WCDMA) or Timing Advance (TA) in Global System for Mobile communications (GSM) and LTE, or UE Rx-Tx time difference(in LTE) in each grid point.        Quantized noise rise, representing the load of a Code Division Multiple Access (CDMA) system, in each grid point.        Quantized signal quality e.g. RxQual in GSM, Ec/NO in WCDMA and Reference Signal Received Quality (RSRQ) in LTE.        Radio connection information like the radio access bearer (RAB).        Quantized time.        
It is noted that the tag consist of a vector of indices, each index taking an enumerable number of discrete values. Continuous variables used for tagging, like path loss, hence need to be quantized.
Step 2: Collect all high precision positioning measurements that have the same tag in separate high precision measurement clusters, and perform further processing of said cluster in order to refine it. Geographical region can be smaller than the extension of a cell of the cellular system.
Step 3: A polygon that represents the geographical extension of a cluster is computed, for each stored high precision position measurement cluster. The two most pronounced properties of the algorithm include:                The area of the polygon is minimized (accuracy hence maximized).        The probability that the terminal is within the polygon (the confidence) is precisely known (it is set as a constraint in the algorithm).        
Step 4: For an incoming positioning request, the UE's network measurement is firstly obtained. By looking up cell Ids or tags, the polygon corresponding to the determined tag is then looked up in the tagged database of polygons, followed by reporting, e.g. over Radio Access Network Application Part (RANAP) using the polygon format.